This invention relates to an optical network element (hereafter called an O-NE), which is optical transmission equipment for use in an all-optical network using multiplexing/demultiplexing routing based on optical wave length, and to an optical transmission method.
Recently, as the amount of data traffic has increased rapidly, a need has arisen for a higher, larger-capacity transmission network. Conventionally, a network element (hereafter called an NE) for use on a transmission network has used Time Division Multiplexing (hereafter called TDM). To process a large volume of transmission data, an NE using Wavelength Division Multiplexing (WDM) has become popular on a network. The introduction of WDM has led an O-NE to employ not only optical wavelength multiplexing but also optical wavelength switching and routing.
FIG. 1 is a diagram showing an optical wavelength division multiplexing equipment (hereafter called WDM) which is an O-NE. The WDM wavelength-multiplexes the optical signal xcex1(optical wavelength: xcex1), optical signal xcex2, . . . , and optical signal xcexn transmitted from the tributary side through n optical fibers to optical signals (optical wavelength: xcex1xcx9cxcexn and sends them to one aggregate fiber. The WDM demultiplexes the multiplexed optical signals (optical wavelength: xcex1xcx9cxcexn) from the aggregate side.
In this specification, the swung dash (xcx9c) is used to indicate wavelength-multiplexed signals, and the ellipses (. . . ) to indicate signals not wavelength-multiplxed.
In addition to the WDM, there are other O-NEs: an Optical Add-Drop Multiplexer (hereafter called OADM) and an Optical Cross-Connect (hereafter called OXC).
FIG. 2 shows the OADM. The OADM receives wavelength-multiplexed optical signals (optical wavelength: xcex1xcx9cxcexn) from the West aggregate side and, with the use of the optical drop function, drops optical signals xcexi and xcexj onto the tributary side. The OADM passes signals with other wavelengths. At the same time, the OADM receives the optical signals xcexi and xcexj from the tributary side and, with the optical add function, and adds and wavelength-multiplexes them to the West aggregate side or East aggregate side. The OADM processes optical signals from the East aggregate side (optical wavelength: xcex1xcx9cxcexn) in the same way it processes the signals from the West aggregate side.
FIG. 3 is a diagram showing the OXC. The OADM has one fiber connected to each aggregate side, while the OXC has multiple fibers connected to each aggregate side. The OADM adds and drops optical signals only on a wavelength level, while the OXC adds and drops optical signals not only on a wavelength level but also on an optical fiber level. This allows the OXC to cross-connect optical signals on a large scale. To do so, it sometimes requires the function to perform optical wavelength conversion.
FIGS. 4, 5, and 6 show some examples in which an all-optical network using O-NEs is built. Routing paths, which have been set up electrically in the conventional network, are set up optically in the all-optical network. This means that the all-optical network can handle a large number of broad-band signals. One of the problems with building the all-optical network is the number of multiplexed wavelengths in WDM.
The optical wavelength used for WDM is defined by ITU-T as about 1550 nm. The number of multiplexed wavelengths using this wavelength is approximately 40 or so, with the maximum being 80-100. For optical path routing in the all-optical network, one wavelength is assigned to transmission from one end customer to another end customer. Therefore, the number of wavelengths is a bottleneck of building a large network. Especially, in a backbone network where a large number of optical signals are received from access networks, the limit on the number of wavelengths is a serious problem.
Earlier patent disclosures relating to the present invention are found in Japanese Patent Application No. Hei 2-162939 (U.S. Pat. Nos. 5,144,466 and 5,343,314) and in Japanese Patent Application No. Hei 7-30771. However, the problem described above is not described in these patent applications. The optical cross-connect and optical ADM technology are described in xe2x80x9cIntegrated Lightwave Networksxe2x80x9d (FUJITSU 48, 5, 436-411).
In view of the foregoing, it is an object of the present invention to provide optical transmission equipment, that is an O-NE, and optical transmission method which solve the problems involved in building a large optical network and which help to build an efficient and economical all-optical network.
In the all-optical network, optical signals from the nodes of end customers are routed at an optical wavelength level to form a network. An optical signal itself has various bit rates. In SDH/SONET networks, low-speed systems use 50 Mb/s, 150 Mb/s, and 600 Mb/s, and high-speed systems use 2.4 Gb/s and 10 Gb/s. In non-SDH/SONET networks, low-speed units use 45 Mb/s, 100 Mb/s, and 200 Mb/s and high-speed units use 1 Gb/s. The bit rate of many optical signals from end customer nodes in access networks, for example, from those in SDH/SONET networks, is 2.4 G/s or lower. The bit rate of most signals is 600 Mb/s or lower.
When these optical signals are transmitted over an optical network, many optical wavelengths are necessary because each optical signal requires its own optical wavelength. This makes it difficult to build the network. In addition, in a case of allocating a low bit rate to an optical wavelength, it is not economical in terms of transmission capacity because the optical wavelength originally capable of transmitting a high-speed signal is used for a low-speed signal.
In view of the foregoing, the O-NE according to the present invention multiplexes a plurality of relatively low-speed optical signals in the TDM mode to convert them to a high-speed electrical signal. A new type O-NE is provided according to the present invention, which has a function of converting the electrical signal to an optical signal with another optical wavelength in order to solve the above-described problem. The O-NE according to the present invention is called Optical Gateway Equipment.